A protester throws a tear gas canister during clashes with police near Tahrir Square in Cairo. The unrest began on the second anniversary of the revolution that toppled Hosni Mubarak.

Photo: Khalil Hamra, Associated Press

A protester throws a tear gas canister during clashes with police...

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Egyptians carry the coffin of a man killed during a mass funeral in Port Said, Egypt, Sunday, Jan. 27, 2013. Tens of thousands of mourners poured into the streets of the restive Egyptian city of Port Said on Sunday for a funeral for most of the 37 people killed in rioting a day earlier, chanting slogans against Islamist President Mohammed Morsi. (AP Photo)

Photo: Str, Associated Press

Egyptians carry the coffin of a man killed during a mass funeral in...

Port Said, Egypt -- President Mohamed Morsi invoked emergency powers in three cities Sunday night to stem riots that have killed more than 50 people and raised questions over whether his Islamic-backed government can secure order amid sharpening political turmoil.

In a nationally televised address, Morsi shook his finger at the camera and warned, "Those who try to scare citizens, use weapons, block roads, throw rocks at the innocent, those who attempt to jeopardize the safety and security of this nation, we must deal with them with all force and firmness."

The emergency powers impose curfews for 30 days in the country's most troubled cities: Ismailia, Port Said and Suez. The army deployed to the towns over the weekend after rioting and looting threatened businesses, public institutions and ports near the Suez Canal. But violence continued as gunmen roamed streets of closed shops and blowing garbage.

Seven people were killed and more than 600 were injured in Port Said on Sunday when police and mourners exchanged gunfire during a funeral procession for those who died in violence a day earlier. Clashes also erupted for a fourth straight day in Cairo, where protesters burned tires and blocked the 6th of October Bridge near a stretch of tourist hotels.

The latest wave of unrest began Friday on the second anniversary of the revolution that toppled longtime autocrat Hosni Mubarak. The violence intensified Saturday, when 21 soccer fans were sentenced to death in Port Said for killing rival fans in a riot last year. Their relatives attempted to storm the prison, clashing with police. At least 33 people died.

Bitterness at Morsi and his Muslim Brotherhood party over the nation's deteriorating security and economic chaos was resonant.

"This country has been in a worsening state for 10 years. We had hoped Morsi's new government would improve things," said Sameh Abd Khalek, an accountant in Port Said. "Morsi has not responded to our needs. I don't know what the solution is. But people just don't curse the police anymore, they're cursing Morsi too."

The new violence has raised concerns over whether the government can impose order and calm political passions before the economy collapses. The police, once the symbol of Mubarak's oppression, have been accused of using excessive force and are increasingly the target of public rage.

Morsi's decision to enact limited emergency measures also raised fears among activists that the country would again slide toward martial law.